The overall objective of the project is to provide a fundamental mechanistic basis for the rational design of therapeutic measures to prevent or ameliorate the pathological consequences of lipid oxidation, for example, by blocking the formation of certain toxic products that damage the retina resulting in age-related macular degeneration. Our immediate goal is to understand oxidative fragmentation reactions of polyunsaturated fatty acyl derivatives that generate a complex mixture of oxidatively truncated phospholipids (oxPCs) and aliphatic lipid fragments. These fragmentation products exhibit diverse and often pathological biological activities. Mutagenic epoxyalkenals and cytotoxic hydroxyalkenals are of particular interest. Knowledge of the chemistry of the reactive intermediates involved in their generation is important for understanding how environmental or genetic factors can promote their formation. Our recent observations showed that exposure to intense light generates significant levels of biologically active oxPCs in rat retinas, and demonstrated that oxPCs can be produced through non free radical pathways that involve singlet, i.e., photoexcited, oxygen. Although the generation of singlet oxygen has been suspected of having pathological significance, an understanding of the molecular basis of the consequent retinal pathology is sorely lacking. [unreadable] The project focuses on studying key intermediates that are not stable under the oxidative fragmentation reaction conditions. Three basic questions will be addressed: (1) are the putative intermediates actually involved, and if so (2) what products are generated by their decomposition and (3) by what mechanism(s) do they fragment? In some cases, they will be trapped as stable derivatives to confirm their involvement. To provide ample quantities of some reactive intermediates, unambiguous total syntheses will be designed and executed. The authentic samples will be used as standards for establishing methods to detect and quantify levels of the intermediates in oxidation reaction product mixtures and in vivo. Their generation and conversion into toxic or innocuous end products will then be investigated. We will determine the influences of (1) environments such as those found in different organelles or associated with pathological conditions, (2) levels of cofactors, or (3) oxidation initiating systems and inhibitors, on the production of the reactive intermediates and on the relative importance of various pathways for their subsequent transformations. [unreadable] [unreadable] [unreadable]